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Adding a small common mode choke with low interwinding capacitance upstream of an offline SMPS cannot possibly make the radiated emissions scan any worse?
If conducted emissions and radiated emissions
"share the same energy source" and you cut the
conducted emissions by adding a choke (pair),
where does the "surplus" go now?
exactly - the emissions now radiate out the output wires - or more directly from the case - any answer is difficult without detailed knowledge of the exact set up ...
Radiation is caused by AC currents in a conductor.
If you block the conducted EMI from AC currents at the input, then it will also reduce the radiation from that source.
But if the conducted currents now find a different path, such as the output, then the EMI could still be there or worse.
You may need common-mode chokes on the output as well as the input, besides shielding of the circuit, to meet both conducted and radiated EMI requirements.
Thnaks, supposing the SMPS is enclosed in an earthed enclosure, which obviosuly having a mains cable going into it, and a isolated dc cable coming out of it. Also, all holes in this enclosure are far smaller in dimension than the problem frequencies, wich are up to 200MHz.
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